Sheet producing or sheet coating apparatus



June 4, 1963 E. G. GoULD ETAL SHEET PRODUCING OR SHEET COATING APPARATUS Filed April 14, 1960 2 Sheets-Sheet l www @W June 4, 1963 E. G` GOULD ETAL SHEET PRODUCING OR SHEET COATING APPARATUS Filed April 14, 1960 2 Sheets-Sheet 2 r||+ l l l l l l l.'

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assises Patented' June 4, 1963 3,091,800 SHEET PRGDUClNG R SHEET COATENG APPARATUS Eric Gordin Gould, Wylde Green, Sutton Coidield, and

.lohn Biggs, Four Oaks, Sutton Coldiield, England, assignors to Dunlop Rubber Company Limited, London, England, a British company lFiied Apr. 14, 1960, Ser. No. 22,301 Claims priority, appiication Great Britain Apr. 22, 1959 11 Claims. (Cl. 13 2) Our invention relates to controls for calenders having a pair of parallel, spaced, rotating, rolls or bowls forming a nip through which plastic material passes to form a sheet of material. The plastic is formed into a sheet either alone or accompanied by a backing sheet passed through the nip with the plastic in known manner. Our invention controls the spacing of the rolls or bowls to produce a sheet of uniform thickness or weight per unit area.

It has heretofore been known to provide a calender with a nip control motor which operates under control of a gauge, such as a beta-ray gauge, to adjust the nip of the calender rolls so as to maintain substantially constant the thickness of the iilm of rubber or other plastic material on one or more of the bowls of the calender.

According to the invention, a sheet producing or sheet coating apparatus comprises a sheet-thickness control system operated by a gauge for measuring deviations in either direction from a predetermined standard of the thickness or weight per unit area of a sheet of material, said system being inoperative so long as the deviation of the thickness or weight per unit area of the sheet in either direction from a predetermined standard does not exceed a predetermined iirst limit, the control system acting for a short period of predetermined length in the appropriate direction to reduce the deviation when the deviation exceeds said iirst limit and for a longer period of predetermined length in the appropriate direction to reduce the deviation when said deviation exceeds a second and larger predetermined limit.

Preferably, for example in a calender, in order to avoid correcting non-persistent errors, arising for example from feed Variations or eccentricity of a Vbowl or bowls of the calender, the system includes a time delay circuit which prevents operation of the control system until the error persists and the deviation exceeds the irst of said limits for a predetermined time. It is also desirable that a sequence delay circuit should be incorporated to prevent operation of the control system for a predetermined period following each action thereof, in order to ensure that further corrections are not made until the effect of the previous correction has `been established.

Preferably also an extra motor run is applied, on the lirst occasion that an error changes sign after a previous correction, to take up any backlash in the motor control system. Subsequent corrections of the same sign do not have this additional motor run.

One embodiment of a calender control system according to the invention is illustrated by way of example in the accompanying drawings in which:

FIGURE l is a diagram illustrating a typical control sequence, and

FIGURE 2, is a block diagram of the system.

FIGURE. 2 shows the -system as applied to the control of an electrically controlled driving means in the form of a nip motor for adjusting the nip between the lower pair of bowls 11 of a four bowl calender for reducing -to a sheet of predetermined thickness a strip 12 of rubber fed into position between the bowls. The motor 10 operates a pair of lead screws, one at each end of the calender and connected together by suitable gearing, to simultaneously 2 alter the nip at each end of the calender. This mechanism is well known and has been omitted for clarity.

The system includes gauging means in the form of a pair of beta-ray back-scatter gauges of well known form, each comprising a source of beta-rays to direct radiation on to the material to be tested and an ionisation chamber to detect the quantity of radiation back-scattered, in the case of gauge 14 from the material, FIG. 2, and, in the case of gauge 13, from the calender bowl and the material thereon. One gauge 13 measures the weight ofthe rubber iilm on the upper of the two bowls 11 and the other gauge 14 tests the entering strip 12. A composition control unit 15 of the kind `described in U.S. patent to Gough, 2,988,- 641, June 13, 1961, compares the signals from the two gauges 13, 14 and applies to an amplifier 16 signals which are indicative of variations in weight of the rubber film and are unaffected by changes in composition of the rubber.

Referring now to FEGURE l, this shows at the left hand side a graph indicating variations in weight of the iilm of rubber and at the right hand side the pulses applied by the system to the nip mot-or 10.

At point A the indicated weight is crossing the positive inner limit 101 into the dead zone 102 following a previous correction to close the nip to reduce `the weight of the film.

Nothing further happens until at B, the weight exceeds the limit 1011 and after the error persist check, a short motor run -is applied, closing the nip, followed by the sequence `delay to allow lthe gauge 13 to indicate the altered weight. The disturbance causing the weight to increase rbeyond the limit was a large one 4and this correction is therefore insuiiicient, for at C the weight exceeds the outer limit 103, the sequence delay period is reduced and :a long motor run is applied followed again by the sequence ydelay time. This is sutlicient to reduce the weight and at D it passes inside the outer limit 103. The sequence delay time then ends and a short motor run is applied which is suliicient to reduce the weight into the dead zone 102. All control action now ceases for so long as the weight deviation' is inside this dead zone.

At point F, the yweight becomes too light and passes the negative inner limit 104. As in the previous case there is first the error persist check but the first motor run following is increased by the amount required to take up backlash in the nip drive. This is necessary because the direction of rotation of the nip screw has been reversed. The sequence delay follows the correction and another normal short motor run occurs until the weight passes the negative outer limit at G. The sequence -delay time is reduced by the initiation of a long motor run which is also reduced as the weight passes inside the limit at H. Short motor runs follow ytill at K it again enters the dead zone. At L the weight passes temporarily outside the positive inner limit 101 but stays there for less than the error persist time so no vaction is taken.

The other notable feature short motor runs, the third enters the dead zone.

Reverting -to FIGURE 2, it will be seen that the system includes an on-olf switch 1'7 and a reversing means in the form of a switch 18 for the nip motor 10. Associated with the amplitier 16 are four schmitt trigger circuits 19-22 forming actuating means for the motor 10. A tirst pair of circuits 20, 21 of the circuits 19 -to 22 respond respectively to positive Iand negative deviations in weight beyond the inner limits 101 and 104 respectively and the second pair of circuits 19, 22 responds to positive and negative deviations in weight beyond the outer limits 103 and 105 respectively. Schmitt trigger circuits are described in Time Bases, pages 8l, 82, by

is at N where after two is out short as the Iweight O. S. Puckle, published by Chapman and Hall (London),

A timing system for the nip motor is controlled by the circuits 19-22 and consists of further Schmitt trigger circuits, viz. a circuit 23 which controls the duration of the shout motor runs, `a circuit 24 which controls the duration of the long motor runs and a circuit 25 which controls the sequence delay time between motor runs. It will be noted (see I-l, FIGURE 1) that the sequence delay time is interrupted when the weight passes out-side either of the outer limits 103 or 105. Preceding the circuits 23 and-25 are two valve relay circuits, one for positive and the other for negative correction, contained in the block 26 and providing the error persist check. A circuit in :the block 27 detects the sign of the error and adjusts the reversing switch 18 accordingly and a circuit in the block 28 alters the time const-ant of the circuit 23, when necessary, to increase the duration of the short motor runs to take up backlash in the nip drive system.

Circuits are provided for interrupting a long motor run when the deviation has been reduced to a level within the outer :limits and a short motor run when the deviation has been reduced to a level within the inner limits, and circuits tare also provided for over-riding the sequence delay timer to start a long motor run whenever a deviation exceeds an outer The control system according to the invention is applicable to all types of calender and, indeed, to the control cf any other apparatus, eg. apparatus incorporating an adjustable doctor blade for controlling thickness, for producing a sheet of material or a single thickness coating on a sheet of material.

Having now described our invention', what We claim is:

l. Apparatus for controlling the nip between the rolls of a sheeting calender to limit the variations in thickness of a sheet produced by the calender comprising gauging means for generating electrical signals which vary with variations in the weight per unit area of the calendered sheet, an electrically controlled driving means for drivable connection to a pair of rolls of a calender for adjusting the nip between said pair of rolls, an actuating means for the driving means connected to the gauging means an'd operable by electric signals received therefrom when the deviation in weight per unit area of the calendered sheet exceeds a predetermined first limit, a reversing means for the driving means in series between the actuating means and the driving means and responsive to the sense of the signal from the gauging means for driving the driving means in the appropriate direction to reduce a deviation in said weight of calendered sheet, a timing system operable by the actuating means for limiting, lfor a period of predetermined length, the actuation of the driving means when the deviation exceeds said first -predetermined limit and for limiting, for a relatively lon-ger period of predetermined length, the actuation of the driving means when the deviation exceeds a second and larger predetermined limit, and a sequence delay circuit operable to isolate the driving means for `a predetermined period following each operation thereof. Y

2. Apparatus 4for controlling the rolls of a sheeting calender to limit the variations in thickness in the sheet produced which comprises gauging means for generating electric energy varying with Yvariations in the weight per unit area of the calendered sheet, an electrically controlled motor to move said rolls alternately toward or from each other, a iirst pair of electric circuits in parallel triggered by said electric energy, one circuit of said rst pair of circuits being triggered at alower level of electric energy generated by said gauging means and the other circuit of said iirst pair of circuits being triggered at a higher 'level of electric energy, a circuit in series with said iirst pair of circuits and comprising a sequence delay circuit and a timing system to control said motor for a predetermined period of time, a second pair of electric circuits in parallel with one another and in parallel with the first pair of circuits, one circuit of said second pair of circuits being triggered by said electric energy below the lower level of said iirst pair of circuits and the other circuit of saidV second pair of circuits being triggered at a level of electric energy above the higher level of said first pair of circuits, and a circuit in series with said second pair of circuits, in panallel with said circuit which is in series with the rst pair of circuits, and comprising a timing system to actuate said motor for a predetermined period of time longer than that or said lirst pair ot circuits, and -a reversing circuit controlled by electric energy alternatively from said inner circuit to reverse said motor.

3. The apparatus of claim 2 having an error persist check device in series with said iirst pair of electric circuits and said timing system to prevent actuation of the motor until the electrical energy generated by the engaging -means has been below said lower level or above said higher level for a predetermined time.

4. Apparatus for controlling the nip between the rolls of a sheeting calender to limit the variations in thickness of a sheet produced by the calender which comprises gauging means for generating electrical signals which vary Iwith variations in the weight per unit area of the calendered sheet, an electrically controlled means for adjusting the nipA between the pair of calender rolls, a first pair of parallel circuits controlled by the signals `from said gauging means when the output of said gauging means reaches a lower level of electric energy, one of said circuits being energized by a negative output and the other by a positive output of said gauging unit, a circuit in series with said pair of parallel circuits and comprising a first timer for interrupting said circuit after a preset time, a second pair of parallel circuits controlled by the signals when said gauging means reaches a higher level of electric energy than that required for said rst circuit one of said circuits being energized by a negative output and the other by a positive output of said gauging unit, a circuit in series lwith said second pair of parallel circuits land comprising a second timer for interrupting `said circuits after a longer time period than that of said iirst timer, each Vsaid circuit, both said iirst and second circuits being connected to said means -for adjusting the nip between the pair of calender rolls to control alternatively said adjusting means.

5. rl"he apparatus of claim 4 in which said rst and second parallel circuits each comprises a trigger element to pass an electric current therethrough at an electric energy level imparted by said gauging means, the electric energy level being higher for the trigger elements of the first parallel circuits,

6. Apparatus according to claim 1 Iwherein a delay circuit is incorporated in series with the energizing means to prevent operation of the driving means until said deviation has exceeded the rst of said limits for a predetermined time.

7. Apparatus according to claim 1 wherein the sequence delay circuit is rendered inoperative when the thickness or weight per unit area of the sheet exceeds the said second limit.

8. Apparatus according to claim 1 comprising means for extending the period of energiz-ation of the driving means following a deviation which is in the opposite direction to -an immediately preceding deviation.

9. Apparatus according to claim 1 wherein the gauging means is a backscatter beta-ray gauge.

l0. Apparatus according to claim 1 wherein the actuating means comprises four trigger circuits said circuits being mounted in parallel and being provided one for each of said limits and for each direction, to be actu-fated by the output from the gauge when said output reaches -a level corresponding to a deviation exceeding the corlresponding limit, said trigger circuits operating a timing system for actuating said control system for a short or a long period, `according to which of the four trigger ycircuits is actuated.

11. The `apparatus of claim 1, comprising a circuit in series with reversing circuit and said time limit circuit to alter said time limit circuit after reversal of said motor.

References Cited in the le of this patent UNITED STATES PATENTS Ziffer Mar. 6, 1962 

1. APPARATUS FOR CONTROLING THE NIP BETWEEN THE ROLLS OF A SHEETING CALENDER TO LIMIT THE VARIATIONS IN THICKNESS OF A SHEET PRODUCED BY THE CALENDER COMPRISING GAUGING MEANS FOR GENERATING ELECTRICAL SIGNALS WHICH VARY WITH VARIATIONS IN THE WEIGHT PER UNIT AREA OF THE CALENDERED SHEET, AN ELECTRICALLY CONTROLLED DRIVING MEANS FOR DRIVABLE CONNECTION TO A PAIR OF ROLLS OF A CALENDER FOR ADJUSTING THE NIP BETWEEN SAID PAIR OF ROLLS, AN ACTUATING MEANS FOR THE DRIVING MEANS CONNECTED TO THE GAUGING MEANS AND OPERABLE BY ELECTRIC SIGNALS RECIEVED THEREFROM WHEN THE DEVIATION IN WEIGHT PER UNIT AREA OF THE CALENDERED SHEET EXEEDS A PREDETERMINED FIRST LIMIT, A REVERSING MEANS FOR THE DRIVING MEANS IN SERIES BETWEEN THE ACTUATING MEANS AND THE DRIVING MEANS AND RESPONSIVE TO THE 